Reanning And Dyeing Effect Of Amphoteric Functional SMA On Chrome-tanned Leather

Styrene-maleic anhydride copolymer(SMA)is a kind of typical conventional binary copolymer product,which is widely used in many industrial fields.The sodium salt of SMA is also widely used in leather retanning process as a retanning agent,which also shows unique retanning properties.Due to the existence of a large number of carboxyl anions in the molecular structure,the surface of the retanned leather fibers shows strong electronegative property,which will cause certain color loss in the late dyeing process of leather with anion dye.It also has a negative effect on the absorption and fixation of dyeing and finishing materials of other anionic types of leather.In this study,the molecular structure design was used as the starting point,N-N dimethylethanolamine(DEMA)was used to modify SMA,and amphoteric functionalized SMA sodium salt(SMA-DEMA-Na)was used as the retanning agent in the retanning process of chrome leather,and then the retanning leather was dyed.The effect of SMA-DEMA-Na on chrome-tanned leather was studied.In order to theoretically explore the chemical mechanism of the influence of amphoteric functionalized SMA sodium salt on the absorption and binding effect of chrome tanned leather on anionic dyeing and finishing materials,the system of superfine crushed retanned leather was used to simulate the retanned leather.Firstly,a series of amphoteric SMA derivatives were prepared by esterification modification using p-toluene sulfonic acid(PTSA)as catalyst and DEMA as modifier in N,N-dimethylformamide(DMF)solvent system.In this process,taking esterification rate as the index,the influence of reaction conditions on esterification reaction was studied,and the optimum synthesis conditions were selected.The structure of esterification products was characterized by infrared spectroscopy(FT-IR)and gel permeation chromatography(GPC).The isoelectric point(pI)of esterification products was obtained by means of the variation of Zeta potential in solution.The results showed that the optimal conditions for synthesizing SMA-DEMA were 500%solvent,1.5%catalyst,100℃ reaction temperature,and 8 h reaction time.The correctness of molecular structure was verified by FT-IR.The results of GPC showed that the average molecular weight of SMA was 2459,and that of SMA-DEMA was 2938-4849,and their molecular weight distribution coefficients were about 1.5.With the increase of the amount of DEMA,the isoelectric points of the series products,SMA-DEMA-0.3、SMA-DEMA-0.6、SMA-DEMA-1,were respectively 2.11,4.49,6.23.Secondly,the sodium salts of SMA-DEMA series products were applied to the retanning process of chrome tanned leather,and the retanning effect of amphoteric SMA products on chrome tanned collagen fibers was investigated using shrinkage temperature(Ts),isoelectric point(pI),mechanical properties,thermogravimetry/microthermogravimetry(TG/DTG)and scanning electron microscopy(SEM)as the indexes.The effect of retanning on the dyeing property of chrome-tanned collagen fibers with anionic dye was investigated by the change of dyeing rate of acid dye.The experimental results showed that,compared with SMA,the chromium-tanned collagen fibers after retanning with amphoteric SMA products have improved the stability of hygrothermal,and have good filling properties,tensile strength increased by 29.31%,thermal stability and microscopic dispersion of the leather fibers increased obviously.The isoelectric points of chrome tanning leather,SMA-Na retanning leather,SMA-DEMA-0.3-Na retanning leather,SMA-DEMA-0.6-Na retanning leather,SMA-DEMA-1-Na retanning leather were 6.41,3.76,4.87,5.54,6.32,which can be seen that the amphoteric retanning agent significantly improves the electropositivity of fiber surface.The dyeing rate of acid blue was only 91.50%,while that of SMA-DEMA-Na was 97.52%,which was slightly lower than that of pure chrome tanned leather(98.21%).This indicated that SMA-DEMA-Na retanning agent maintained the original excellent properties of SMA resin retanning agent.It can significantly improve the decolorization of leather fibers.Finally,the chrome tanned leather,SMA-Na and SMA-DEMA-Na retanned leather were superfinly crushed,and the crushed leather fibers were used to simulate the adsorption and desorption experiments on the conventional anionic dyeing and finishing materials(dye and extract).Taking the adsorption capacity as the measurement index,the single factor experiment method was used to optimize the adsorption conditions of various kinds of leather fibers on acid blue dye,direct yellow dye,wattle bark extract and tannic acid extract.The adsorption kinetics and thermodynamic equations of the adsorption process were fitted by combining the adsorption capacity data with the adsorption conditions,and the adsorption mechanism of different leather fibers on the two dyeing and finishing materials was clarified.The experimental results showed that:(1)the adsorption capacity of dyes and tannin extract was obviously better in the leather of SMA-DEMA-Na retanned,but lower than that of pure chrome tanned leather due to structural reasons,indicating that amphoteric functional SMA retanning agent was beneficial to the absorption and binding of anionic dyeing and finishing materials;(2)the fitting results of kinetic and thermodynamic equations showed that the adsorption process of dye/extract on leather fibers could be described by quasi second-order kinetic equation,indicating that chemical adsorption was the main adsorption process.The thermodynamic process is closer to the Langmuir adsorption isothermal model,which indicates that the adsorption process is mainly monolayer adsorption;(3)after the adsorption of dyes and extracts by the three kinds of leather fibers,the isoelectric points on the surface of the leather fibers decreased significantly,and the thermal stability was improved,indicating that the binding process of dyes and extracts with the leather fibers was a multi-component process mainly characterized by chemical action.